In many situations, it is desirable (but not necessary) for lighting to be activated as soon as a person/object of interest enters a particular area of interest. This can be accomplished by using occupancy and/or motion sensors to monitor the area of interest. When a sensor detects occupancy and/or motion, e.g., based on radiation or a change in radiation emitted in the area of interest, it sends a signal to a lighting fixture that causes the lighting fixture to illuminate the area of interest. The lighting fixture illuminates the area for as long as the sensor detects an occupant. As soon as the sensor stops detecting the occupant, a timer in the lighting fixture begins counting down a predetermined timeout or delay period during which the light remains on. The lighting fixture turns off when the delay period ends (unless the occupancy sensor detects another occupant, in which case the timer stops counting down). Consider, for example, a sensor whose timeout period is 60 seconds: if a person enters the sensor's field-of-view at 11:27:03 and stays in the field-of-view until 11:31:18, the light remains on until 11:32:18 provided that nobody else enters the field-of-view. If the predetermined timeout or delay period is too long, then the light remains on unnecessarily, wasting energy and running down its useful life. If the predetermined amount of time is too short, then the light turns off prematurely, which may be annoying and possibly dangerous as well.
Occupancy sensors sense radiation at different wavelengths, including infrared, ultrasonic, visible, and/or radio-frequency wavelengths, to detect the presence or absence of people in a space. Passive infrared (PIR) sensors sense the difference in heat emitted by humans in motion from that of the background space. These sensors detect motion within a field of view that generally requires a clear line of sight; they cannot “see” through obstacles and have limited sensitivity to minor (hand) movement at distances greater than about 15 feet. PIR sensors tend to be most sensitive to movement laterally across their respective fields of view, which can be adjusted when the sensor is installed.
PIR sensors generally are most suitable for smaller, enclosed spaces (wall switch sensors), spaces where the sensor has a view of the activity (ceiling- and wall-mounted sensors), and outdoor areas and warehouse aisles. Potentially incompatible application characteristics include low motion levels by occupants, obstacles blocking the sensor's view, mounting on sources of vibration, or mounting within six feet to eight feet of HVAC air diffusers.
Ultrasonic sensors use the Doppler principle to detect occupancy by emitting an ultrasonic high-frequency signal (e.g., 32-40 kHz) throughout a space, sensing the frequency of a signal reflected by a moving object, and interpreting a change in frequency as motion. The magnitude and sign of the change in frequency represent the speed and direction, respectively, of the object with respect to the sensor. Ultrasonic sensors do not require a direct line of sight and instead can “see” around corners and objects, although they may need a direct line of sight if fabric partition walls are prevalent. In addition, ceiling-mounted sensor effective range declines proportionally to partition height. Ultrasonic sensors are more effective for low motion activity, with high sensitivity to minor (e.g., hand) movement, typically up to 25 feet. Ultrasonic sensors tend to be most sensitive to movement towards and away from the sensor. Ultrasonic sensors typically have larger coverage areas than PIR sensors.
Ultrasonic sensors are most suitable for open spaces, spaces with obstacles, restrooms, and spaces with hard surfaces. Potentially incompatible application characteristics include high ceilings (greater than 14 feet), high levels of vibration or air flow (which can cause nuisance switching), and open spaces that require selective coverage (such as control of lighting in individual warehouse aisles).
Dual-technology sensors employ both PIR and ultrasonic technologies, activating the lights only when both technologies detect the presence of people, which virtually eliminates the possibility of false-on. Dual-technology sensors keep the lights on so long as they continue to detect the presence of people using at least one of the two sensing technologies, which significantly reduces the possibility of false-off. Appropriate applications include classrooms, conference rooms, and other spaces where a higher degree of detection may be desirable.
For effective occupancy sensing, generally required coverage area and required sensitivity are coordinated by a lighting designer/engineer. Generally the designer must determine range and coverage area for the sensor based on the desired level of sensitivity. Manufacturers of sensors publish range and coverage area for sensors in their product literature, which may be different for minor (e.g., hand) motion and major (e.g., full-body) motion. Various coverage sizes and shapes are available for each sensor type. In a small space, one sensor may easily provide sufficient coverage. In a large space, it may be desirable to partition the lighting load into zones, with each zone controlled by one sensor.
The lighting designer/engineer must also decide how long each light should remain on after the associated occupancy and/or motion sensor no longer detects motion. This timeout parameter is controlled typically in hardware, so the designer may have only a few discrete options, e.g., 30 seconds, one minute, two minutes, five minutes, etc., for a particular type of lighting fixture. The operating characteristics and requirements of the lighting fixtures often determine the minimum timeouts. For example, fluorescent and high-intensity discharge (HID) fixtures have relatively long warm-up times, so they may have minimum timeouts of about 10-15 minutes to minimize wear and tear that would otherwise reduce the fixture life.
The timeout parameter is controlled typically by setting a switch (e.g., dual in-line package (DIP) switches), dial, or other interface on the lighting fixture itself. Once the lighting fixture is installed, it may become difficult to change the timeout settings (if they can be changed at all). For example, industrial lighting fixtures, such as the high-bay lighting fixtures that illuminate aisles in a warehouse, are often too high to be reached without a lift. Even if the fixture is relatively easy to reach, it may be impractical to change the timeout parameter because the people who own, maintain, and/or use the facility have no way to determine the appropriate or optimum timeout setting.
U.S. Patent Application Publication No. 2007/0273307 to Westrick et al. discloses an automated lighting system that performs adaptive scheduling based on overrides from users. More specifically, Westrick's system follows a predetermined schedule to switch a lighting fixture from an “ON” mode (in which the fixture turns on in response to a signal from an occupancy sensor) to an “OFF” mode (in which the fixture does not respond to signals from the occupancy sensor). Firmware adjusts the amount of time the system spends in “ON” mode based on how often users override the lighting controls by actuating an override switch, such as an on/off paddle switch. If the system detects a high number of overrides immediately after a period in “ON” mode, the system increases the amount of time that the system is “ON” (and decreases the amount of time that the system is “OFF”). Although Westrick's system adjusts how long a light is enabled to respond to occupancy signals, it does not change how long the light remains on in response to an occupancy signal. It also requires direct user intervention. Westrick's system does not log or record any occupancy sensor data, so it is incapable of detecting, analyzing, and responding to more complicated occupancy behavior, such changes in occupancy patterns based on the hour of the day or the day of the week.
U.S. Pat. No. 8,035,320 to Sibert discloses an illumination control network formed of luminaires whose behaviors are governed by a set of parameters, which may be selected from templates or set by direct user intervention. Sibert's luminaire has an occupancy response behavior that depends in part on a high threshold, a low threshold, and a decaying average, or running average, that represents the average output level from an occupancy sensor over a recent time interval. When the luminaire receives a signal from the occupancy sensor, it updates the running average, then compares the updated running average to the high and low thresholds. If the updated running average is lower than the low threshold, the luminaire remains off (or turns off). If the updated running average is higher than the high threshold, the luminaire turns on (or remains on) for a predetermined timeout period. If the updated running average is between the high and low thresholds, the luminaire remains in its current state until it receives another signal from the occupancy sensor or, if the luminaire is already on, until the timeout period elapses. The luminaire does not adjust the length of the timeout period in response to an occupancy signal. Like Westrick's system, Sibert's luminaires do not log or record any occupancy sensor data, so they are cannot detect, analyze, or respond to more complicated occupancy behavior, such changes in occupancy patterns based on the hour of the day or the day of the week.